Joba Chamberlain‘s rehab appears to be going well following Tommy John Surgery last June. He gave an update on Twitter the other day and said that he is throwing from flat ground with Larry Rothschild and feels great.
Recovery from TJS typically takes 12-18 months, but some guys do come back in 11. From all of the updates that Joba has given it certainly sounds like he could be a 11-month guy. It is important to keep expectations realistic though, if the Yankees get anything from him by the All-Star break it should be looked at as bonus.
There is no reason to rush him back either as the Yankees have quite the full bullpen as well. Besides the great Mariano Rivera, they still have David Robertson, Rafael Soriano, and depending on how things shake out the next month or two Phil Hughes could be joining them.
A bullpen of Mo, Robbie, Soriano and Hughes is ridiculous.
Tell Joba to take his time!
Don't expect a significant contribution from Joba until 2013. He'll pitch in 2012, but there's little reason for the Yankees to rush him back. They'll gradually increase his pitches in game action sometime after the All-Star break, but they'll go slow and pick their spots. Considering how full the bullpen is, they'll probably have him take the full 21-day recovery period in the minors, before he starts seeing MLB game action in August. If the Yankees are lucky, his command will be there and he can help the team down the stretch, but a major impact from him won't happen until next year.
Unless he takes a step back in his rehab at some point I think you are being a little unrealistic. It's not like they have to build him back into a starter. It doesn't take long to stretch a pitcher out to 15 pitches, especially if he's already throwing off flat ground. I'd say a week rehabbing, maybe 2. Unless the bullpen is really packed to the point where there is no room for him, he'll be back quickly. My guess is first half of June.